When cells are stressed, the highly conserved catabolic pathway called macroautophagy is upregulated. The upregulation of this pathway induces the formation of autophagosomes, distinct compartments that target proteins and organelles for degradation. The high demand for membrane to make autophagosomes during cell stress leads to a dramatic reorganization of intracellular membranes. Consequently, the secretory pathway is downregulated and membrane from the secretory pathway is redirected to the macroautophagy pathway. The recent finding that ER-derived COPII coated vesicles are a membrane source for autophagosome formation suggests that the down regulation of the secretory pathway during cell stress is the result of diverting COPII vesicles from the ER-Golgi pathway to the macroautophagy pathway. Understanding how COPII vesicles are redirected from their canonical route to an alternate pathway is critical to elucidating a 40 year mystery in the autophagy field, the initiation of the membrane reorganization events that occur when macroautophagy is induced. In this proposal I present three specific aims to address the role that phosphorylation plays in targeting COPII vesicles to the macroautophagy pathway. 1. We have identified three patches of phosphorylation sites on the COPII coat that are important for cellular viability. A variety of approaches will be used to determine if the phosphorylation of one or more of these sites plays a role in diverting a COPII vesicle to the macroautophagy pathway. 2. We will identify the kinases that redirect COPII vesicles to the macroautophagy pathway. These studies are likely to define the connection between the kinases that redirect traffic to the macroautophagy pathway and the TORC1 interaction network that regulates the induction of macroautophagy. 3. We have identified a domain in the ER-Golgi tether, Uso1/p115, that is critical for directing a COPII vesicle to the Golgi. We will determine if phosphorylation of this domain facilitates the redirection of COPII vesicles to the autophagic pathway.